Systems for utilizing tidal motion and current flow of oceans and rivers are known. Such systems usually require a dam or other physical structure which separates one part of a water body from another part. A difference in water levels is thereby created which provides a pressure differential useful for driving mechanical devices as hydroturbine generators.
Conventional hydroturbine technology, involving the necessity of positioning a powerhouse in a dam body with turbines located below the lowest water surface, has been applied at large river and waterfall sites. However, the hydroenergy potential of thousands of small rivers and river canals remain untapped because hydroturbines, as an economical and practical matter, do not operate effectively with a low water head, in other words, when water level differences are about three meters or less. Hydroturbines need significant water depth for installation and cost-efficient operation. Consequently, powerhouses which contain the hydroturbines must be installed in large and complicated dam structures capable of withstanding the enormous water pressures generated.
Systems for harnessing the energy in ultra low water heads (less than three meters) and in smaller scale systems employing pneumatic turbines and devices are also known. In U.S. Pat. No. 4,103,490, issued to the same inventor as herein, a single tidal chamber is utilized in which a housing is mounted on the ocean bed with ports of ingress and egress near the bottom or lower part of the housing, through which tidal waters may flow. Positive air pressure is built up in the housing by rising tides, and partial vacuums are created by falling tides. The positive air pressure or partial vacuum at the top of the housing is connected through auxiliary high pressure and low pressure chambers to a two-state revolving valve having two input ports and two output ports. The output ports may be connected to a reciprocating air motor so that low level energy in the last one foot or so of the tide may be made to do useful work.
In U.S. Pat. No. 4,095,423, also issued to the same inventor, a similar system is described in which a dam structure is used, but an air valve rather than a water valve is employed.
In U.S. Pat. No. 4,464,080, also issued to the same inventor as herein, an apparatus is described for utilizing power generated by rising and falling tides or by flowing currents. A single cavity chamber contains a high volume gating system in which water is cyclically gated from the high water level on one side of a dam, through the single cavity chamber, to the lower water level on the other side of the dam, alternately providing positive air pressure and a partial vacuum within the single chamber. Air pressure variations are used for driving an air motor. In one embodiment, the chamber comprises a barrier at the chamber bottom which divides the bottom of the chamber in half, large ports on either side of the barrier to permit alternative inflow and outflow of high volumes of water, and mechanically operated sets of sluice gates for selectively opening and sealing different sets of ports. Also disclosed are vertical sluice gates that are automatically activated by their own weight and water pressure.
The present application represents a patentable development of the concept of using an air engine to harness hydropower. This concept was formulated by the Applicant in U.S. Pat. Nos. 4,095,423; 4,103,490; and 4,464,080 described above.
A double-box system has been devised at the Coventry Polytechnic Institute, England, which is comprised of a butterfly- or figure-eight-shaped pair of hydro-pneumatic chambers which are connected together by a diverting vertical valve. Upstream water flows against one side of the figure "8" and is diverted into one of the chambers, while water in the other chamber is allowed to flow into downstream water on the other side. The valve is a vane which pivots on a vertical axis to control the water input and output of the two chambers. Switching the valve causes the chambers to fill and empty alternatively which drives air through a turbine coupled to an electric generator to produce electric power. However, this double box system requires an external mechanical drive to switch the diverting valve. The drive must provide sufficient torque to overcome the inertia of the valve as well as of the swept water and suction forces generated. The torque must also be sufficient to switch the valve in seconds, so as to maintain the water level gradient created between the two chambers, and can therefore consume considerable output power. The mechanical complexity of the valve and drive system gives rise to reliability problems. Even if automatic switching mechanisms can be adapted to the vertically-pivoting diverting gate, the use of such a gate does not permit high volumes of water to be processed because the large gates required for processing large volumes of water have greater inertia and water resistance, thereby increasing cycle times. Because a single vertical gate is used for both chambers, unavoidable loss of water and potential energy arises due to direct leakage of the water flow out of both chambers when the gate is in an intermediate position. These characteristics disfavor application of such a gate design to a harnessing system intended for use with low water heads.